US10770086B2 - Zero-latency pulse density modulation interface with format detection - Google Patents
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- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L19/02—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using spectral analysis, e.g. transform vocoders or subband vocoders
- G10L19/032—Quantisation or dequantisation of spectral components
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L19/005—Correction of errors induced by the transmission channel, if related to the coding algorithm
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L19/008—Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
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- H03F3/183—Low frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only
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Definitions
- the present disclosure relates in general to circuits for audio devices, including without limitation personal audio devices such as wireless telephones and media players, and more specifically, to systems and methods for automatically detecting a format of a pulse density modulation signal with zero latency.
- Personal audio devices including wireless telephones, such as mobile/cellular telephones, cordless telephones, mp3 players, and other consumer audio devices, are in widespread use.
- Such personal audio devices may include circuitry for driving a pair of headphones or one or more speakers.
- Such circuitry often includes a power amplifier for driving an audio output signal to headphones or speakers.
- PDM pulse density modulation
- Some audio systems utilize “1.5-bit” encoding in which, for each audio channel, datagrams of two bits are used to encode three quantization levels, with one two-bit code being an invalid code.
- some audio systems use 2-bit encoding in which, for each audio channel, datagrams of two bits are used to encode four quantization levels.
- two or more audio channels of a signal are encoded in a single PDM data stream, with alternating datagrams representing each channel in the data stream (e.g., a two-bit datagram representing a left audio channel, followed by a two-bit datagram representing a right audio channel, followed by a two-bit datagram representing the left audio channel, followed by a two-bit datagram representing the right audio channel, and so on).
- audio data in PDM format may be communicated via a single electrical conduit (e.g., package pin, trace, wire, cable, etc.).
- a transmitter e.g., a processor
- a receiver e.g., a Class-D amplifier
- detection methods are needed to determine the boundaries of PDM datagrams (e.g., determining where within the data stream a most-significant bit of a datagram is located) as well as determining which audio channel each PDM datagram is associated.
- one or more disadvantages and problems associated with existing approaches to processing of multi-bit PDM data may be reduced or eliminated.
- a method may include receiving a stream of serial pulse-density modulation (PDM) data representing a first channel of data synchronized with a rising edge of a clock associated with the serial PDM data and a second channel of data synchronized with a falling edge of the clock, wherein each of the first channel of data and the second channel of data include encoded datagrams wherein each encoded datagram comprises more than one digital bit, detecting an invalid state associated with the stream, and responsive to detecting the invalid state, determining boundaries of each encoded datagram of the stream based on where within the stream the invalid state occurred.
- PDM serial pulse-density modulation
- a system may include an input configured to receive a stream of serial pulse-density modulation (PDM) data representing a first channel of data synchronized with a rising edge of a clock associated with the serial PDM data and a second channel of data synchronized with a falling edge of the clock, wherein each of the first channel of data and the second channel of data include encoded datagrams wherein each encoded datagram comprises more than one digital bit.
- PDM serial pulse-density modulation
- the system may also include a processing subsystem configured to detect an invalid state associated with the stream and responsive to detecting the invalid state, determine boundaries of each encoded datagram of the stream based on where within the stream the invalid state occurred.
- FIG. 1 is an illustration of an example personal audio device, in accordance with embodiments of the present disclosure
- FIG. 2 is a block diagram of selected components of an example audio integrated circuit of a personal audio device, in accordance with embodiments of the present disclosure
- FIG. 3 is a block diagram of selected components of an example processing subsystem of a Class-D amplifier, in accordance with embodiments of the present disclosure
- FIG. 4 illustrates a table showing various parameters that may be applied by a processing system based on a configuration of an audio integrated circuit in accordance with embodiments of the present disclosure
- FIG. 5 illustrates example clock waveforms that may be generated by a processing subsystem, in accordance with embodiments of the present disclosure.
- FIG. 6 illustrates example clock and signal waveforms that may be generated by a processing subsystem, in accordance with embodiments of the present disclosure.
- FIG. 1 is an illustration of an example personal audio device 1 , in accordance with embodiments of the present disclosure.
- FIG. 1 depicts personal audio device 1 coupled to a headset 3 in the form of a pair of earbud speakers 8 A and 8 B.
- Headset 3 depicted in FIG. 1 is merely an example, and it is understood that personal audio device 1 may be used in connection with a variety of audio transducers, including without limitation, headphones, earbuds, in-ear earphones, and external speakers.
- a plug 4 may provide for connection of headset 3 to an electrical terminal of personal audio device 1 .
- Personal audio device 1 may provide a display to a user and receive user input using a touch screen 2 , or alternatively, a standard liquid crystal display (LCD) may be combined with various buttons, sliders, and/or dials disposed on the face and/or sides of personal audio device 1 . As also shown in FIG. 1 , personal audio device 1 may include an audio integrated circuit (IC) 9 for generating an analog audio signal for transmission to headset 3 and/or another audio transducer.
- IC audio integrated circuit
- FIG. 2 is a block diagram of selected components of an example audio IC 9 of a personal audio device, in accordance with embodiments of the present disclosure.
- example audio IC 9 may be used to implement audio IC 9 of FIG. 1 .
- PDM generator 14 may generate a PDM input signal PDMDATA, a pulse-width modulated signal based on an input signal INPUT.
- PDM generator 14 may also generate a clock signal CLK indicating the synchronization of data communicated within PDM input signal PDMDATA.
- One or more Class-D amplifiers 16 may receive PDM input signal PDMDATA and clock signal CLK and output a modulated output signal that may be filtered by a low-pass filter 22 to generate an analog output signal which may be driven to a transducer (e.g., one or more of speakers 8 A and 8 B) for playback of audio sound.
- a transducer e.g., one or more of speakers 8 A and 8 B
- PDM input signal PDMDATA may have encoded therein datagrams for audio to be played back to two different audio output channels.
- a first Class-D amplifier 16 may receive PDM input signal PDMDATA and clock signal CLK and process only data associated with its audio channel in order to output a modulated output signal V DRV_L that may be filtered by a low-pass filter 22 to generate an analog output signal V OUT_L which may be driven to a transducer (e.g., speaker 8 A) for playback of audio sound, and a second Class-D amplifier 16 may receive PDM input signal PDMDATA and clock signal CLK and process only data associated with its audio channel in order to output a modulated output signal V DRV_R that may be filtered by a low-pass filter 22 to generate an analog output signal V OUT_R which may be driven to a transducer (e.g., speaker 8 b ) for playback of audio sound.
- a transducer e.g., speaker 8 b
- audio IC 9 as being a two-channel stereo audio system
- audio IC 9 and the systems and methods described herein do not apply to only a two-channel stereo audio system, but may generally be applied to a single-channel (e.g., mono) system, dual-channel (e.g., stereo) system, or multi-channel (e.g., 5.1 surround sound, 7.1 surround sound) system.
- single-channel e.g., mono
- dual-channel e.g., stereo
- multi-channel e.g., 5.1 surround sound, 7.1 surround sound
- FIG. 3 is a block diagram of selected components of an example processing subsystem 30 of a Class-D amplifier (e.g., a Class-D amplifier 16 ), in accordance with embodiments of the present disclosure.
- processing subsystem 30 may include a clock generation block 32 for generating a local clock signal PDM_CLK_PHASE at a phase relative to clock signal CLK received by processing subsystem 30 and a PDM data generation block 34 .
- output logic 36 of PDM data generation block 34 generates a PDM output signal PDM_OUT (which is depicted as a two-bit datagram in FIG.
- PDM output signal PDM_OUT may have any suitable bit width), based on a configuration of audio IC 9 (e.g., number of audio channels, bit width, etc.), as well as output a signal PDM_IF_PHASE_SEL that indicates an output of the PDM signal based on the phase of the local clock PDM_CLK_PHASE.
- Clock generation block 32 may receive the signal PDM_IF_PHASE_SEL, and the logic of clock generation block 32 may, for configurations in which the bit width of input signal PDMDATA is two or more (e.g., for 1.5 bit or higher signal resolution), may detect if an invalid state is detected for the phase of the local clock PDM_CLK_PHASE (which indicates that the local clock is not properly aligned with the data stream), and if so, may correct and update the local clock to properly align with the data stream, thus performing automatic format detection of the incoming PDM data.
- such invalid state may be determined by the signal PDM_IF_PHASE_SEL having an invalid code.
- such invalid state may be determined by the signal PDM_IF_PHASE_SEL having an invalid transition (e.g., an invalid transition for successive datagrams associated with a channel).
- FIG. 4 illustrates a table showing various parameters that may be applied by processing subsystem 30 based on a configuration of audio IC 9 , in accordance with embodiments of the present disclosure.
- FIG. 5 illustrates example clock waveforms that may be generated by processing subsystem 30 , in accordance with embodiments of the present disclosure.
- processing subsystem 30 may generate a clock signal having a waveform of a particular frequency (denoted by “1 ⁇ ” under clock rate in FIG. 4 , and represented by waveform 50 in FIG. 5 ), and with a local clock PDM_CLK_PHASE being delayed 180 degrees from clock signal CLK (represented by waveform 58 of FIG. 5 ).
- Class-D amplifier 16 and PDM generator 14 should not be misaligned, and thus automatic format detection may be disabled, as indicated by the word “OFF” in the “AUTO DETECT” column in FIG. 4 .
- local clock PDM_CLK_PHASE may be adjusted to an active edge of clock signal CLK, and generated with a 180-degree phase shift with respect to clock signal CLK.
- processing subsystem 30 of a first channel may generate a clock signal having a waveform of the same frequency applied for the single-bit, single-channel configuration (denoted by “1 ⁇ ” under clock rate in FIG. 4 , and represented by waveform 50 in FIG. 5 ), and with a local clock PDM_CLK_PHASE being delayed 180 degrees from clock signal CLK (represented by waveform 58 of FIG. 5 ).
- processing subsystem 30 of a second channel may generate a clock signal having a waveform of the same frequency applied for the single-bit, single-channel configuration (denoted by “1 ⁇ ” under clock rate in FIG. 4 , and represented by waveform 50 in FIG. 5 ), and with a local clock PDM_CLK_PHASE having no delay from clock signal CLK (represented by waveform 54 of FIG. 5 ).
- Class-D amplifier 16 and PDM generator 14 should not be misaligned, and thus automatic format detection may be disabled, as indicated by the word “OFF” in the “AUTO DETECT” column in FIG.
- local clock PDM_CLK_PHASE of the first channel may be adjusted to an active edge of clock signal CLK, and generated with a 180-degree phase shift with respect to clock signal CLK, while local clock PDM_CLK_PHASE of the first channel may be adjusted to an active edge of clock signal CLK, and generated with no phase shift with respect to clock signal CLK.
- processing subsystem 30 may generate a clock signal having a waveform of the same frequency applied for the single-bit, single-channel configuration (denoted by “1 ⁇ ” under clock rate in FIG. 4 , and represented by waveform 50 in FIG. 5 ), and with a local clock PDM_CLK_PHASE having no delay from clock signal CLK (represented by waveform 54 of FIG. 5 ).
- Class-D amplifier 16 and PDM generator 14 should not be misaligned, and thus automatic format detection may be disabled, as indicated by the word “OFF” in the “AUTO DETECT” column in FIG. 4 .
- local clock PDM_CLK_PHASE may be adjusted to the least-significant bit of input signal PDMDATA. If the most-significant bit is sent on the negative edge of clock signal CLK and the least-significant bit on the positive edge of clock signal CLK, then local clock PDM_CLK_PHASE should have no phase shift with respect to clock signal CLK.
- processing subsystem 30 of a first channel may generate a clock signal having a waveform of twice the frequency applied for the single-bit, single-channel configuration (denoted by “2 ⁇ ” under clock rate in FIG. 4 , and represented by waveform 52 in FIG. 5 ), and by default may generate a local clock PDM_CLK_PHASE being delayed 270 degrees from clock signal CLK (represented by waveform 60 of FIG.
- processing subsystem 30 of the first channel may modify the local clock to be delayed 90 degrees from clock signal CLK (represented by waveform 56 of FIG. 5 ).
- processing subsystem 30 of a second channel e.g., the right channel, indicated by the row “STEREOR 1.5-BIT” in FIG. 4
- processing subsystem 30 of the second channel may modify the local clock to be delayed 180 degrees from clock signal CLK (represented by waveform 58 of FIG. 5 ).
- processing subsystems 30 may determine boundaries of each encoded datagram of the data stream of signal PDM_DATA based on where within the stream the invalid code occurred. Also of note is that in each case, the local clocks PDM_CLK_PHASE of the two channels are 180 degrees out of phase, meaning that encoded datagrams for one channel are sampled on a rising edge of a clock, and encoded datagrams for another channel are sampled on a falling edge of the same clock.
- local clock PDM_CLK_PHASE for each channel may be set to a default phase.
- Processing subsystem 30 of each channel may search for an invalid code, and detection of an invalid code may indicate the default setting for phase was incorrect, and then local clock PDM_CLK_PHASE for each channel may be modified to align the clock to capture data at the earliest time possible. For example, consider a scenario in a dual-channel, 1.5-bit configuration in which the code “10” is invalid for a datagram.
- a processing subsystem 30 may search for two consecutive bits having the value “10.” If “10” occurs respectively at a least-significant bit of one datagram and the most-significant bit of the subsequent datagram, such detection may indicate a correct setting for the default clock phase. However, if “10” occurs respectively at a most-significant bit of one datagram and the least-significant bit of the same datagram, such detection may indicate an incorrect setting for the default clock phase, and processing subsystem 30 may respond by modifying the phase of its local clock PDM_CLK_PHASE. FIG.
- processing subsystem 30 may modify the local clock to be delayed 180 degrees from clock signal CLK (represented by waveform 58 of FIG. 5 ) and may insert an appropriate delay into clock signal PDM_CLK_X as shown in FIG. 6 .
- example processing subsystem 30 of FIG. 3 (and FIGS. 4-6 further illustrating its operation) is one which can handle various configurations of the data stream of signal PDM_DATA, including one-channel or dual-channel configurations, and configurations in which the data stream of signal PDM_DATA comprises single-bit datagrams or dual-bit datagrams representing three quantization levels.
- processing subsystem 30 may detect for the occurrence of an invalid transition between one or more bits of successive datagrams for a particular channel.
- example processing subsystem 30 of FIG. 3 could be additionally modified in accordance with this disclosure to apply to systems having more than two channels of audio data.
- this disclosure may disclose a method (and system for performing the method) comprising receiving a stream of serial PDM data representing a first channel of data synchronized with a rising edge of a clock associated with the serial PDM data and a second channel of data synchronized with a falling edge of the clock, wherein each of the first channel of data and the second channel of data include encoded datagrams wherein each encoded datagram comprises more than one digital bit.
- the method may further include, detecting an invalid state associated with the stream.
- the method may also include responsive to detecting the invalid state, determining boundaries of each encoded datagram of the stream based on where within the stream the invalid state occurred.
- the method may additionally include, responsive to detecting the invalid state, modifying the clock to align with the boundaries of each encoded datagram.
- modifying the clock to align with the boundaries of each encoded datagram may comprise modifying the clock such that a PDM output delay for a PDM interface circuit configured to receive the stream is approximately zero.
- the number of quantization levels represented by an encoded datagram may be equal to a power of two of the number of bits in the encoded datagram and detecting the invalid state comprises detecting an invalid transition between successive datagrams of one of the first channel and the second channel. In these and other embodiments of the method, the number of quantization levels represented by an encoded datagram is less than a power of two of the number of bits in the encoded datagram and detecting the invalid state comprises detecting an invalid datagram in one of the first channel and the second channel.
- references in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. Accordingly, modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the disclosure. For example, the components of the systems and apparatuses may be integrated or separated.
- each refers to each member of a set or each member of a subset of a set.
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US5682162A (en) * | 1994-12-27 | 1997-10-28 | Burr-Brown Corporation | Oversampling digital-to-analog converter with auto-muting feature |
US20160044412A1 (en) * | 2011-05-27 | 2016-02-11 | Cirrus Logic International Semiconductor Ltd. | Digital signal routing circuit |
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US5682162A (en) * | 1994-12-27 | 1997-10-28 | Burr-Brown Corporation | Oversampling digital-to-analog converter with auto-muting feature |
US20160044412A1 (en) * | 2011-05-27 | 2016-02-11 | Cirrus Logic International Semiconductor Ltd. | Digital signal routing circuit |
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